Conventionally, the development of a system which has a sensor module installed in a tire air space of a vehicle or the like, and which collects tire environment related physical quantities such as air pressure and temperature to inform the driver of deterioration of the environment in real time, has been energetically performed.
Generally, the sensor module is constituted by using an electronic circuit and hence needs electric power supply. However, the sensor module is installed in the tire air space in most cases, and the power supply to the sensor module from the outside of the tire is difficult. Thus, in many cases, the sensor module is driven by using a battery.
However, since it takes much time to replace the battery in the battery drive, a device for supplying electric power to the tire, which can substitute for the battery, is also developed (Japanese Patent Publication 2004-23904). This device comprises: a stator which is provided for a non-rotating part of an axle and forms a magnetic field; a rotor which is fixed to a rotating part of the axle, rotates in the magnetic field and generates an electromotive force; and a power transmission part which transmits the electromotive force generated by the rotor to an in-space apparatus. Further, in the stator, N poles and S poles which form the magnetic field advancing to the axle center are alternately arranged on a circumference around the axle center. The rotor comprises: a plurality of rotating yokes, each of which has one end fixed to the rotating part of the axle at a position corresponding to the stator in the axle axial direction and the other end positioned near the inside and in the radial direction of the stator, and is formed of a high-permeability magnetic material; coupling yokes which magnetically couple the rotating yokes; and rotating coils which are spirally wound around the rotating yokes along the axle radial direction to generate electromotive forces in accordance with the rotation of the axel.
Further, power generating devices which generate electric power by providing a piezoelectric element in a tire are also developed (WO03/095244, WO03/095245). These devices are constituted in such a manner that a structural body having a piezoelectric element formed in a fiber-like state is embedded in the tire to enable electric power to be outputted from the piezoelectric element by deformation of the piezoelectric element caused by the deformation of the tire.
[Patent document 1]: Japanese Patent Publication 2004-23904
[Patent document 2]: WO03/095244
[Patent document 3]: WO03/095245